Optical imaging or spectroscopy systems and methods

ABSTRACT

Optical imaging or spectroscopy described can use laminar optical tomography (LOT), diffuse correlation spectroscopy (DCS), or the like. An incident beam is scanned across a target. An orthogonal or oblique optical response can be obtained, such as concurrently at different distances from the incident beam. The optical response from multiple incident wavelengths can be concurrently obtained by dispersing the response wavelengths in a direction orthogonal to the response distances from the incident beam. Temporal correlation can be measured, from which flow and other parameters can be computed. An optical conduit can enable endoscopic or laparoscopic imaging or spectroscopy of internal target locations. An articulating arm can communicate the light for performing the LOT, DCS, or the like. The imaging can find use for skin cancer diagnosis, such as distinguishing lentigo maligna (LM) from lentigo maligna melanoma (LMM).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/087,979, filed Mar. 31, 2016, which is a continuation of U.S. patentapplication Ser. No. 12/655,325, filed Dec. 29, 2009 (now U.S. Pat. No.9,655,523), which is a continuation under 35 U.S.C. 111(a) of PCT PatentApplication PCT/US2008/008081, filed Jun. 27, 2008, which claims thebenefit of the following three US provisional patent applications:Application 60/937,724, filed Jun. 29, 2007; Application 61/000,792,filed Oct. 29, 2007; and Application 61/130,904, filed Jun. 4, 2008.Each of the above-identified applications is incorporated herein byreference in its entirety

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH

This invention was made with government support under grant numberNS053684 awarded by the National Institutes of Health (NIH). TheGovernment has certain rights in this invention.

Additional support was received from the Wallace H. Coulter Foundation.

BACKGROUND

There are both clinical and non-clinical applications for imaging anobject of interest. In a clinical example, a body part may be imaged intwo or three dimensions in various ways, such as by using radiation(e.g., X-ray or CT imaging), magnetism (e.g., magnetic resonanceimaging), sound (e.g., ultrasound imaging), or light (e.g., opticalcoherence tomography). Spectroscopic information is also useful, such asfor determining the composition of an object of interest.

OVERVIEW

The present inventors have recognized, among other things, that laserscanning microscopy can presently only achieve penetration depths ofless than 600 μm, because of light scattering effects. Laser scanningmicroscopy also often uses an exogenous fluorescent contrast agent thatis introduced into the object to enhance the resulting image. Ifthree-dimensional (3D) images are to be acquired, laser scanningmicroscopy serially adjusts the focal plane of the light to sampledifferent depths within the object, however, this can be time-consuming.

The present inventors have also recognized that laminar opticaltomography (LOT) allows depth-resolved, non-contact imaging of an objectsuch as living tissue at high frame rates, and such as to depths ofgreater than 2 mm with up to 100 to 200 μm resolution. Unlike laserscanning microscopy, LOT concurrently obtains information about variousdepths in parallel, rather than serially. LOT can image absorptioncontrast (such as oxyhemoglobin, deoxyhemoglobin, or melaninconcentration) as well as fluorescence. For example, LOT can be appliedto in-vivo dermal imaging of skin cancer or in-vivo imaging of thefunction of a rat brain. The LOT techniques can be performed atorthogonal or oblique angles, such as described further below.

The present inventors have further recognized that a technique of usingLOT to acquire images at multiple wavelengths (e.g., so as to be able todistinguish between multiple different light-absorptive substances) canuse respective shutters to modulate light from corresponding individuallasers emitting light at different wavelengths. However, the presentinventors have also recognized that this can dramatically slow downimage acquisition speed and can limit the number of wavelengths, typesof light sources, or types of data that can be acquired.

Accordingly, the present inventors have recognized and developed atechnique that allows multi-spectral LOT data to be acquired inparallel, such that data at one wavelength can be acquired concurrentlywith data at another (different) wavelength. Among other things, thismeans that multiple lasers—or even a broadband light source such as anLED or a lamp—can be used to concurrently illuminate the tissue withdifferent wavelengths of light. Moreover, by a clever arrangement of thedetection configuration, each wavelength can be distinguished andrecorded concurrently—in addition to allowing the concurrentdepth-resolved LOT data. In such a parallel or concurrent mode, imageacquisition can proceed as fast as scanning of an incident beam allows.This can be quite fast and may generally merely be limited bygalvanometer mirror scanning speed, digital data acquisition rate, orthe noise floor of the light detector. Furthermore, discrete wavelengthlaser sources can be very expensive, and will typically provide only asmany different distinct wavelengths as the number of lasers. Bycontrast, the present systems or methods permit use of one or morebroadband sources or multi-wavelength lasers to potentially allowconcurrent imaging of detailed depth-resolved spectral optical responseinformation. For fluorescence imaging, the present systems or methodsallow the full spectrum of the fluorescent emission to be measured, ifdesired. One or more excitation wavelengths can be used concurrently,while one or more different fluorophores can be measured anddistinguished concurrently. Multiple concurrent measurements of thefluorescence emission spectrum can be recorded, allowing forspectroscopic analysis as well as imaging using the present techniques.

Thus, the present inventors believe that the present techniques canprovide dramatic improvements to the efficacy, speed, and potentialapplications of LOT. Examples of potential applications include, withoutlimitation, fluorescence and absorption contrast imaging or spectroscopyof living tissues, such as the brain, retina, skin, or endothelialtissues, such as the oral mucosa, colon, or cervix. By concurrentlyacquiring multi-spectral absorption or fluorescence measurements, rapidfunctional imaging can be accomplished.

The present inventors have also recognized that the present techniquescan be used concurrently with diffuse correlation spectroscopy(DCS)—which can benefit from the scanning and other aspects of thepresent techniques. The DCS information can be used to directly orindirectly provide additional useful information, such as blood flow,tissue oxygenation, oxygen metabolism, or the like. This is particularlyuseful where the region of interest includes brain tissue, for example,such as for ischemic or stroke characterization. For example, absorptioncontrast can provide oxygenation information, which, combined with DCS,can yield metabolism information. Certain examples in this documentdescribe a combined LOT/DCS system that is capable of concurrentlyquantifying (1) absorption (and hence oxyhemoglobin and deoxyhemoglobindynamics in living tissue), (2) fluorescence (such as that from acalcium sensitive or voltage sensitive dye, a targeted molecular probe,or an intrinsic fluorophore such as FAD, NADH, or collagen), and (3)blood flow, such as via DCS.

The present inventors have further recognized that the presenttechniques can benefit from using an at least partially flexible opticalconduit to communicate with the target region. For a human or animalsubject, this can permit convenient external or internal imaging of atarget location. In certain examples, such as for internal imaging of abody lumen, 360-degree circumferential viewing can be accomplished, suchas by using a rotatable angled mirror. The rotatable angled mirror canalso be useful in laparoscopic or oral examination, such as forexamining the oral mucosa, for example. A specified separation between adistal portion of the optical conduit and the target region of the bodycan be obtained using an inflatable balloon or other fixed or adjustableseparation device.

The present inventors have further recognized that one approach would beto use a LOT system that is built on a rigid platform, with opticalcomponents steering the laser beam or other light down onto the objectto be imaged. The platform can be raised and lowered, and the objectivelens can be tilted, but its utility can be severely restricted ifimaging is to occur in the clinic where the face and neck are not easilyand comfortably accessible via a rigid platform. Accordingly, thepresent inventors have recognized that, by introducing an articulatingarm, and solving the associated optical and configuration difficultiesof sending and detecting LOT or DCS signals, one can be enabled to imageany area near which one can position the articulating arm. This can helpextend all of the benefits of LOT or DCS to situations in which the LOTor DCS information is to be acquired in a clinic.

In certain examples, the LOT or DCS system including the articulatingarm can allow imaging of skin cancer lesions on the neck and face. Thearticulating arm can be used while still providing the LOT system withcareful control over the off-axis returning light that allowsdepth-resolved LOT imaging (rather than just illumination). Thearticulating arm allows LOT or DCS to be extended to many more clinicalapplications than without the articulating arm, and can provide bettersignal-to-noise characteristics than an endoscopic embodiment. Incertain examples, the LOT or DCS system including the articulating armcan be used in a non-medical imaging application, such as for example inindustrial quality control in difficult to reach places (e.g., wheredepth-resolved imaging of turbid material is desirable). Thearticulating arm can also allow configurations that require delivered ordetected light to retain one or more features that cannot be maintainedduring passage through an optical fiber. In certain examples,transmission of ultra-violet light, pulsed laser light, or polarizedlight can be significantly deteriorated by an endoscopic or otheroptical fiber conduit, as compared to an articulating arm includingsuitable reflectors, such as described further herein.

Example 1 can include subject matter that can comprise at least onelight source providing at least one wavelength of light. In thisexample, the apparatus can comprise a scanner, configured to receive thelight from the light source, and configured to scan a beam of the lightacross a target region. In this example, the apparatus can comprise alight detector, configured to receive from the target region a scanningresponse signal at a plurality of distances from a beam location uponthe target region. In this example, the apparatus can comprise awavelength separator, configured with respect to the light detector todirect a first wavelength of the scanning response signal to a differentlocation of the light detector than a second wavelength of the scanningresponse signal, wherein the second wavelength is different from thefirst wavelength.

In Example 2, the subject matter of Example 1 can optionally comprise asignal processor, coupled to the light detector, the signal processorconfigured to concurrently process the scanning response signal of thefirst wavelength and the scanning response signal of the secondwavelength. In this example, the lateral distances can define a linearfirst direction, and wherein the wavelength separator is configured tospatially separate wavelengths of the scanning response signal in alinear second direction that is orthogonal to the first direction.

In Example 3, the subject matter of any one of Examples 1 or 2 canoptionally comprise the light detector including a two-dimensional arrayof light detector elements, and is configured to detect differentwavelengths of the scanning response signal along a first dimension ofthe two-dimensional array, and to detect along a second dimension of thetwo-dimensional array optical responses from the different lateraldistances from the beam location, and wherein the first and seconddimensions of the two-dimensional array are orthogonal to each other,and comprising an imaging data memory including a two-dimensional arrayof memory locations for corresponding scanning locations of the targetregion, each two-dimensional array of memory locations storing data fromthe two-dimensional array of light detectors for a particular scanninglocation of the target region.

In Example 4, the subject matter of any one of Examples 1-3 canoptionally comprise the light source comprising: a first laser,providing laser light at the first wavelength; and a second laser,providing laser light at the second wavelength that is different fromthe first wavelength, and wherein the first wavelength of the scanningresponse signal is in response to the first wavelength of laser lightprovided by the first laser, and wherein the second wavelength of thescanning response signal is in response to the second wavelength oflaser light provided by the second laser.

In Example 5, the subject matter of any one of Examples 1-4 canoptionally be configured such that the first wavelength of the scanningresponse signal is in response to a first emission wavelength of a firstfluorophore, and wherein the second wavelength of the scanning responsesignal is in response to a second emission wavelength of a secondfluorophore of the same type as the first fluorophore or of a differenttype than the first fluorophore.

In Example 6, the subject matter of any one of Examples 1-5 canoptionally comprise a beam splitter configured to communicate light withthe scanner and the wavelength separator.

In Example 7, the subject matter of any one of Examples 1-6 canoptionally comprise a housing that carries at least the scanner and anobjective lens.

In Example 8, the subject matter of any one of Examples 1-7 canoptionally comprise a tubular spacer, configured to fit about theobjective lens and to maintain a specified distance between theobjective lens and the target region.

In Example 9, the subject matter of any one of Examples 1-8 canoptionally comprise an articulating arm, configured to communicate lightalong the articulating arm, between the housing and the target region,without requiring a fiber optic conduit.

In Example 10, the subject matter of any one of Examples 1-9 canoptionally be configured such that the articulating arm comprises: firstand second elongated segments, each segment defining a longitudinaldirection; a pivot, coupling the first and second elongated segments,wherein at least one of the first and second elongated segments isconfigured to rotate about the longitudinal direction with respect tothe pivot; and wherein the pivot comprises an angled mirror configuredto redirect light from along a longitudinal direction of a first segmentto be along a longitudinal direction of the second segment.

In Example 11, the subject matter of any one Examples 1-10 canoptionally comprise at least two pivots and at least three segments.

In Example 12, the subject matter of any one of Examples 1-11 canoptionally be configured such that the light source comprises abroadband light source.

In Example 13, the subject matter of any one of Examples 1-12 canoptionally be configured such that the wavelength separator includes atleast one of a prism, a diffraction grating, a dichroic filter, ormultiple dichroic mirrors.

In Example 14, the subject matter of any one of Examples 1-13 canoptionally be configured such that the wavelength separator receiveslight from a slit that defines a longitudinal direction such that theplurality of lateral distances from the beam location upon the targetregion correspond to different locations along the longitudinaldirection of the slit.

In Example 15, the subject matter of any one of Examples 1-14 canoptionally comprise: a correlator circuit, coupled to the light detectorto receive and compute a temporal correlation of the scanning responsesignal from the target region; and a signal processor, configured toreceive and use the temporal correlation to compute a firstcharacteristic of the target region.

In Example 16, the subject matter of any one of Examples 1-15 canoptionally comprise the signal processor configured to receive, inresponse to the same scanning, a fluorescence component of the scanningresponse signal, and to use the fluorescence component of the scanningresponse signal to compute a second characteristic of the target region.

In Example 17, the subject matter of any one of Examples 1-16 canoptionally comprise the signal processor being configured to receive, inresponse to the same scanning, an absorption component of the scanningresponse signal, and to use the absorption component of the scanningresponse signal to compute a third characteristic of the target region.

In Example 18, the subject matter of any one of Examples 1-17 canoptionally comprise the signal processor being configured to receive, inresponse to the same scanning, an absorption component of the scanningresponse signal, the absorption component comprising at least twodifferent wavelengths of light, and to use the absorption component ofthe scanning response signal to compute the third characteristic of thetarget.

In Example 19, the subject matter of any one of Examples 1-18 canoptionally comprise: an optical conduit, optically coupled to thescanner and the light detector, the optical conduit configured tocommunicate the beam of the first wavelength of light to the targetregion, and configured to communicate the scanning response signal fromthe target region; and a laparoscopic or endoscopic instrument carryingthe optical conduit.

In Example 20, the subject matter of any one of Examples 1-19 canoptionally be configured such that a distal portion of the conduitincludes a longitudinal-to-side optical translator guide that comprisesa mirror that is obliquely angled with respect to a longitudinal axis ofthe optical conduit.

In Example 21, the subject matter of any one of Examples 1-20 canoptionally be configured such that the mirror is rotatable about thelongitudinal axis of the optical conduit.

Example 22 can include, or can be combined with any one of Examples 1-21to optionally include, subject matter including: sourcing light to forman incident beam; scanning a location of the incident beam across atarget region; obtaining an optical response at different locations atdifferent distances in a first direction from the beam location upon thetarget region; dispersing different wavelengths of the optical response;and detecting the dispersed wavelengths of the optical response from thedifferent locations concurrently to provide information about the targetregion.

In Example 23, the subject matter of any one of Examples 1-22 canoptionally be configured such that sourcing the light includes sourcinglight at different wavelengths.

In Example 24, the subject matter of any one of Examples 1-23 canoptionally be configured such that detecting the dispersed wavelengthsof the optical response includes detecting a first and secondwavelengths of fluorophore emission, wherein the first wavelength offluorophore emission is different from the second wavelength offluorophore emission.

In Example 25, the subject matter of any one of Examples 1-24 canoptionally be configured such that detecting the dispersed wavelengthsof the optical response includes detecting the first wavelength offluorophore emission from a first type of fluorophore and detecting thesecond wavelength of fluorophore emission from a second type offluorophore that is different from the first type of fluorophore.

In Example 26, the subject matter of any one of Examples 1-25 canoptionally be configured such that dispersing different wavelengths ofthe optical response includes dispersing along a linear second directionthat is orthogonal to the first direction at a light detector.

In Example 27, the subject matter of any one of Examples 1-26 canoptionally comprise: storing a two-dimensional array of responseinformation from the light detector for different beam locations of thetarget region; and using the stored two-dimensional array of responseinformation from the light detector for different beam locations of thetarget region to construct at least one of: a three dimensional renderedimage of the target region; an image representing chemical compositionof the target region; and a plurality of images representing informationabout different depths of the target region.

In Example 28, the subject matter of any one of Examples 1-27 canoptionally be configured such that dispersing different wavelengthscomprises refracting different wavelengths by different amounts.

In Example 29, the subject matter of any one of Examples 1-28 canoptionally be configured such that dispersing different wavelengthscomprises diffracting the different wavelengths by different amounts.

In Example 30, the subject matter of any one of Examples 1-29 canoptionally be configured such that dispersing different wavelengthsincludes filtering a first wavelength from a second wavelength.

In Example 31, the subject matter of any one of Examples 1-30 canoptionally comprise: computing, for the multiple different laterallocations, a temporal correlation of the scanning optical response; andcomputing a first characteristic of the target region using the temporalcorrelation.

In Example 32, the subject matter of any one of Examples 1-31 canoptionally comprise obtaining, in response to the same scanning, afluorescence component of the scanning optical response signal; andusing the fluorescence component of the scanning optical response signalto compute a second characteristic of the target region.

In Example 33, the subject matter of any one of Examples 1-32 canoptionally comprise obtaining, in response to the same scanning, anabsorption component of the scanning optical response signal; and usingthe absorption component of the scanning optical response signal tocompute a third characteristic of the target region.

In Example 34, the subject matter of any one of Examples 1-33 canoptionally comprise obtaining, in response to the same scanning, anabsorption component of the scanning optical response signal, theabsorption component comprising at least two different wavelengths oflight; and using the absorption component of the scanning opticalresponse signal to compute a third characteristic of the target region.

In Example 35, the subject matter of any one of Examples 1-34 canoptionally comprise using an optical conduit to communicate light to andfrom the target region.

In Example 36, the subject matter of any one of Examples 1-35 canoptionally comprise scanning an incident beam location and obtaining anoptical response are carried out for a target location that is internalto a human or animal.

In Example 37, the subject matter of any one of Examples 1-36 canoptionally be configured such that scanning an incident beam locationand obtaining an optical response are carried out for a target locationthat is orthogonal to a longitudinal axis of the optical conduit.

In Example 38, the subject matter of any one of Examples 1-37 canoptionally comprise: scanning the location of the incident beam across atarget region comprising skin; and using the information about thetarget region to discriminate between first and second skin conditions.

In Example 39, the subject matter of any one of Examples 1-38 canoptionally comprise using an oblique angle from the target region for atleast one of the scanning or the obtaining the optical response.

These examples can be combined in any permutation or combination. Thisoverview is intended to provide an overview of subject matter of thepresent patent application. It is not intended to provide an exclusiveor exhaustive explanation of the invention. The detailed description isincluded to provide further information about the present patentapplication.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 is a schematic diagram illustrating generally portions of asystem for optical imaging or spectroscopy and portions of anenvironment in which the system can be used.

FIG. 2 is a schematic drawing illustrating generally an example of aninterface apparatus, such as for the system illustrated in FIG. 1.

FIG. 3 is a diagram illustrating generally an example of a method thatpermits concurrently obtaining and separating depth-resolved andspectrally-resolved laminar optical tomography information, such as foruse in imaging or spectroscopy.

FIG. 4 is an example of a plot of absorption vs. wavelength for melanin,HbO₂, and HbR.

FIG. 5 is a schematic drawing illustrating generally an example of asystem, such as for concurrently performing LOT and diffuse correlationspectroscopy (DCS).

FIG. 6 is a diagram illustrating generally an example of portions of amethod that can be performed at least in part by using the system ofFIG. 5, if desired, or another system.

FIG. 7 is a cross-sectional schematic drawing illustrating generally anexample of a distal portion of a laparoscope or endoscope that includean optical conduit.

FIG. 8A is a schematic drawing of an example of a cutaway end view of amirror within an orifice, directing light to and from a region ofinterest.

FIG. 8B is a schematic drawing of an example of the mirror together witha linear arrangement of optical fibers.

FIG. 8C is a schematic drawing of an example of a cutaway side view ofthe mirror and fibers within the orifice.

FIG. 9 is a schematic drawing showing an example in which incident lightis provided through a lens to a polarizing beam splitter that passes Spolarization and reflects P polarization toward a mirror.

FIG. 10A is a color plot of modeled data indicating probability of lightpassing through various regions of tissue, a separation distance of 3.00mm between incident light (at a 15-degree angle from a lineperpendicular to the tissue surface) and a location at which the opticalresponse is observed.

FIG. 10B is a color plot of modeled data indicating probability of lightpassing through various regions of tissue, a separation distance of 2.50mm between incident light (at a 15-degree angle from a lineperpendicular to the tissue surface) and a location at which the opticalresponse is observed.

FIG. 10C is a color plot of modeled data indicating probability of lightpassing through various regions of tissue, a separation distance of 2.00mm between incident light (at a 15-degree angle from a lineperpendicular to the tissue surface) and a location at which the opticalresponse is observed.

FIG. 10D is a color plot of modeled data indicating probability of lightpassing through various regions of tissue, a separation distance of 1.00mm between incident light (at a 15-degree angle from a lineperpendicular to the tissue surface) and a location at which the opticalresponse is observed.

FIG. 10E is a color plot of modeled data indicating probability of lightpassing through various regions of tissue, a separation distance of 0.50mm between incident light (at a 15-degree angle from a lineperpendicular to the tissue surface) and a location at which the opticalresponse is observed.

FIG. 10F is a color plot of modeled data indicating probability of lightpassing through various regions of tissue, a separation distance of 0.20mm between incident light (at a 15-degree angle from a lineperpendicular to the tissue surface) and a location at which the opticalresponse is observed.

FIG. 10G is a color plot of modeled data indicating probability of lightpassing through various regions of tissue, a separation distance of 0.00mm between incident light (at a 15-degree angle from a lineperpendicular to the tissue surface) and a location at which the opticalresponse is observed.

FIG. 11A is a color plot of modeled data indicating probability of lightpassing through various regions of tissue, a separation distance of 4.00mm between incident light (at a 35-degree angle from a lineperpendicular to the tissue surface) and a location at which the opticalresponse is observed.

FIG. 11B is a color plot of modeled data indicating probability of lightpassing through various regions of tissue, a separation distance of 3.00mm between incident light (at a 35-degree angle from a lineperpendicular to the tissue surface) and a location at which the opticalresponse is observed.

FIG. 11C is a color plot of modeled data indicating probability of lightpassing through various regions of tissue, a separation distance of 2.00mm between incident light (at a 35-degree angle from a lineperpendicular to the tissue surface) and a location at which the opticalresponse is observed.

FIG. 11D is a color plot of modeled data indicating probability of lightpassing through various regions of tissue, a separation distance of 1.50mm between incident light (at a 35-degree angle from a lineperpendicular to the tissue surface) and a location at which the opticalresponse is observed.

FIG. 11E is a color plot of modeled data indicating probability of lightpassing through various regions of tissue, a separation distance of 1.00mm between incident light (at a 35-degree angle from a lineperpendicular to the tissue surface) and a location at which the opticalresponse is observed.

FIG. 11F is a color plot of modeled data indicating probability of lightpassing through various regions of tissue, a separation distance of 0.40mm between incident light (at a 35-degree angle from a lineperpendicular to the tissue surface) and a location at which the opticalresponse is observed.

FIG. 11G is a color plot of modeled data indicating probability of lightpassing through various regions of tissue, a separation distance of 0.00mm between incident light (at a 35-degree angle from a lineperpendicular to the tissue surface) and a location at which the opticalresponse is observed.

FIG. 12 shows an example of an articulating arm that can provide opticalcommunication along and within the articulating arm itself.

FIG. 13 shows a schematic illustration of components of the articulatingarm used in conjunction with LOT components.

FIG. 14 shows a schematic illustration of how the lenses and thediffraction grating or other wavelength dispersive element can be usedto spectrally separate the response signal in the z-direction of thetwo-dimensional light detector array, with spatial separation of theoptical response signal being orthogonal thereto, such as in they-direction as shown.

FIG. 15 shows an example of a cross sectional schematic view of skinimaging.

FIG. 16 shows a schematic drawing of an example of a LOT system, such asfor skin imaging.

FIG. 17 shows information relating to skin imaging. The left-most imagesshow Monte-Carlo simulations of the likely paths of light for threesource-detector separations: (1) 0.2 mm, top left image; (2) 0.6 mm,middle left image; and (3) 1.0 mm, bottom left image. The middle imagesshow raw imaging data acquired on a benign mole (A) and amelanoticerythema (B), for the same three source-detector separations. Theright-most images are photographs of the mole (A) and amelanoticerythema (B).

FIG. 18 shows an example of simultaneously-acquired multi-spectral LOTdata obtained using a test phantom as the object being imaged.

DETAILED DESCRIPTION

Optical imaging or spectroscopy described can use laminar opticaltomography (LOT), diffuse correlation spectroscopy (DCS), or the like.An incident beam is scanned across a target. In various examples,time-resolved (e.g., pulsed light) can be used, such as to obtainfluorescence lifetime or scattering information. Frequency modulatedlight can be used, in certain examples. Cross-polarized or otherpolarized light can be used, in certain examples. An optical response tothe incident beam can be obtained, such as concurrently at differentdistances from the incident beam. Such different distances can belinearly displaced from the incident beam, circumferentially displacedfrom the incident beam, or displaced in orthogonal directions from theincident beam location, in various examples. The optical response frommultiple incident wavelengths can be concurrently obtained by dispersingthe response wavelengths in a direction orthogonal to the responsedistances from the incident beam. Temporal correlation can be measured,from which flow and other parameters can be computed. An optical conduitcan enable endoscopic or laparoscopic imaging or spectroscopy ofinternal target locations. An articulating arm can communicate the lightfor performing the LOT, DCS, or the like. The imaging can be used forskin cancer diagnosis, such as distinguishing lentigo maligna (LM) fromlentigo maligna melanoma (LMM).

FIG. 1 is a schematic diagram illustrating generally portions of asystem 100 for optical imaging or spectroscopy and portions of anenvironment in which the system 100 can be used. In this illustrativeexample, the system 100 can include at least one light source, such asone or more of lasers 102, 104, or 106 providing laser light having atleast two different light emission wavelengths. In the illustrativeexample of FIG. 1, the laser 102 emits 635 nm light, the laser 104 emits532 nm light, and the laser 106 emits 473 nm light. In this example, thelight from the multiple light sources of the lasers 102, 104, and 106can be combined and delivered to an optional optical conduit, such as anoptical fiber conduit 108 of one or multiple optical fibers. In thisexample, in which three different wavelengths of light are shown forillustrative purposes, the combining of the different wavelengths oflight can be accomplished using a first frequency/wavelength selectivefilter (e.g., a 45° angled dichroic mirror 110) and a secondfrequency/wavelength selective filter (e.g., a 45° angled dichroicmirror 112). In this example, the dichroic mirror 110 passes lighthaving wavelengths longer than 600 nm (such as the 635 nm light from thelaser 102) and reflects shorter wavelengths (such as the 532 nm lightfrom the laser 104). In this way, the dichroic mirror 110 can be used tocombine the different-wavelength light from the lasers 102 and 104. Inthis example, the dichroic mirror 112 passes light having wavelengthslonger than 500 nm (such as the 635 nm light from the laser 102 and the532 nm light from the laser 104) and reflects shorter wavelengths (suchas the 473 nm light from the laser 106). In this way, the dichroicmirror 112 can be used to combine the different wavelength light fromthe lasers 102, 104, and 106.

In the example of FIG. 1, the optical fiber conduit 108 delivers thecombined different wavelength light from the lasers 102, 104, and 106 toa refractive element, such as a lens 114. The lens 114, in turn,collimates and delivers the combined different wavelength light to abeam-splitter, such as the polarizing beam splitter 116. In thisexample, the beam splitter 116 provides a first portion of this lightalong a first path 118 toward the object to be imaged. This beamsplitter 116 can also serve to direct light returning from the object tobe imaged along a second path 120 toward an imaging detector apparatus,such as described further below.

In the example of FIG. 1, the light provided along the first path 118 isdelivered to an optical scanner 122. In this example, the scanner 122scans its received light across various locations on a two-dimensionalx-y plane. To accomplish this, the scanner 122 can include an x-scannergalvanometer 124 and a y-scanner galvanometer 126, each of which can becomputer controlled. Other techniques of scanning or otherwise steeringthe light can include using an acousto-optical deflector, a polygonalscanning mirror arrangement, a microelectromechanical (MEMs) mirrorarray, or any other suitable light steering technique. In this example,the x-y scanned beam of light that is output by the scanner 122 can beprovided to a refractive element, such as a lens 128, which focuses thescanned light beam at a desired location on a proximal end portion of aflexible optical conduit 130, such as an optical fiber bundle. In thisexample, a distal end portion of the flexible optical conduit 130provides the light to a variable magnifier 132. The variable magnifier132 can include first and second refractive elements 134A-B, having avariable distance with respect to each other or to the distal endportion of the optical conduit 130. The variable magnifier 132 can serveas an objective lens that permits scanning its incident light beamacross a larger (or smaller) field of view, to permit receiving anoptical response signal across the larger (or smaller) field of view.The variable magnifier 132 can also serve to adjust the effectiveseparation between the incident light beam and the detected opticalresponse signal. This allows adjustment of the depth of penetration ofthe incident light beam that is represented by the detected opticalresponse signal. It also allows adjustment of the depth resolutionrepresented by the detected optical response signal. The variablemagnifier 132 need not be located at or near the distal end portion ofthe optical conduit 130, but can alternatively be located at or near theproximal end of the optical conduit 130, or to an intermediate portionof the optical conduit 130, or the variable magnifier 132 can be omittedaltogether, if desired. In certain examples, the lenses 140, 144, or 152can be adjusted to change the separation between the “source” and“detector” light, such as independent of the field of view.

In the example of FIG. 1, the light is delivered to an object to beimaged, such as, for example, a skin lesion site 136 on a person's arm138. An optical response signal can be detected and communicated backalong the first path 118 to the beam splitter 116, and then along thesecond path 120 toward an imaging detector apparatus, such as describedfurther below. This optical response signal can include informationabout one or more of absorbed light (e.g., at the same wavelength as theincident light), reflected light (e.g., at the same wavelength as theincident light), or a fluorescence light emission (e.g., at a differentwavelength than the incident light). The optical response signal neednot occur at the particular location of incidence at which the scannedincident light was delivered. Instead, nearby locations can emit aresponse signal, with locations that are laterally more distant from thelight beam's incident location at the site 136 generally providing anoptical response associated with incident light that has traveled moredeeply into the object to be imaged. Thus, the distance between thelocation of the emitted optical response signal and the location of theincident light is indicative of the depth to which the incident lighthas traveled. Analyzing the optical response signal at multiple suchvarying distances from the location of incidence permits depth-resolvednon-contact imaging of living tissue, which can be referred to as a formof laminar optical tomography (LOT), such as described herein, such asto depths of greater than 2 mm with resolution on the order of about 100to 200 μm, depending on tissue type. The reconstruction analysis can beperformed using modeling such as Monte Carlo simulation, such asdescribed below.

The second path 120 receives light from the beam-splitter 116. In thisillustrative example, a refractive element, such as a lens 140, focusesthe light onto an input of an element comprising a slit 142. An outputof the slit 142 provides the light to a refractive element, in thisexample, such as the lens 144. However, at this point, the opticalresponse light signal does not separate information according towavelength. One approach to separate information by wavelength is toprovide a shuttering mechanism to provide light of a particularwavelength, then analyze the response from that wavelength, and repeatin a time sequence for other wavelengths. However, shuttering istime-consuming such that it is possible that a biological change canoccur before all wavelengths of light are provided and their responsesobserved. In the case of such an intervening biological change, themultiple wavelengths and their responses can fail to provide a uniquespectroscopic solution, can involve using more sophisticated detectioncomponents, or can be slow.

The present inventors have recognized, among other things, that awavelength separator such as a dispersive element 146 can be used in aclever arrangement to solve this problem. In this example, the lens 144collimates and provides the light via a slit to the dispersive element146, such as to a prism, diffraction grating, or one or more dichroicfilters. The slit can be arranged in a first direction (e.g., ay-direction) such that distances along a length of the slit representthe various lateral distances, from the location of instance of theincident light, at which the optical response signal is observed. Thepresent inventors have recognized, among other things, that thedispersive element 146 can be used to disperse the different wavelengthsof the response signal in a second direction (e.g., an “x” direction)that is orthogonal to the first direction of the slit. The resulting x-yarray of wavelength vs. lateral distance optical response informationfrom the dispersive element 146 can be captured using a light detector,such as an x-y photomultiplier array 148, a charge-coupled device (CCD)light detector array, a photodiode array, or a square optical fiberbundle or collection of linear fiber or detector arrays.

In the example of FIG. 1, a reflective element, such as a mirror 150,can optionally be used to direct the light from the dispersive element146 and toward a refractive element, such as a lens 152. The lens 152can be used to provide variable magnification, such as to adjust the x-ydispersion provided by the dispersive element 146 to more fully use thespace provided by the x-y photomultiplier array 148, thereby increasingor maximizing its spectral resolution. Information from the 2D lightdetector array 148 is provided to a computer-implemented or other signalprocessor circuit 160 to perform desired computation or analysis, suchas the Monte Carlo model-based reconstruction described below. Thesignal processor circuit 160 can communicate with a user interface 162,which can include a display, such as to provide information obtainedusing the desired computation or analysis.

LOT using a single wavelength of incident light provides depth-resolvedoptical imaging information. By including the dispersive element 146 inthe LOT system 100, such multiple different wavelengths can be usedconcurrently, and the resulting optical response information can beconcurrently separated according to such different wavelengths. Suchwavelength-separated information can then be processed, such as togenerate a rendered volumetric image or to perform spectroscopicanalysis of the composition of the object being examined. Concurrent useof different wavelengths allows faster imaging or spectroscopy.Information acquisition speed is particularly important for imaging orspectroscopy of biological targets, in which the target otherwise mightundergo a change during the time between imaging or spectroscopy offirst and second different wavelengths, which could potentially render aslower (e.g., serially-obtained) composite of such information useless.Moreover, the present inventors have recognized that concurrent use ofdifferent wavelengths allows use of different light sources. In certainexamples, a cheaper broadband light source (e.g., a light-emitting diode(LED) or a lamp) can replace the laser light sources described above,since the resulting information can be spectrally separated such asdescribed above. Thus, even though FIG. 1 illustrates an example inwhich three different distinct wavelengths of light are used, otherexamples can use fewer distinct wavelengths, (e.g., 2 wavelengths), moredistinct wavelengths (e.g., 4, 5, 6, . . . , etc. wavelengths), or evenmore wavelengths that are not necessarily distinct, such as a broadbandlight source, for example. Thus, FIG. 1 is merely an illustrativeexample; not all components illustrated in FIG. 1 are required in allexamples. Moreover, the present approach using the spectral dispersionof concurrent multiple wavelengths could be cheaper than temporalsequencing of different wavelengths using expensive shutters andseparate lasers for each wavelength instead, an unshuttered lessexpensive single laser concurrently emitting multiple wavelengths oflight can be used, for example.

The present approach can also be useful for observing an exogenous orendogenous fluorescence response, such as in tissue. In an exogenousapproach, a contrast agent, which can include multiple fluorophores thatemit a fluorescence response at different wavelengths, can be introducedinto the tissue. In an endogenous approach, an intrinsic fluorophoreemits the fluorescence response at a different wavelength than theexcitation wavelength. In either an exogenous or endogenous approach, asingle excitation wavelength (or even a broadband light source) can beused to obtain the fluorescent emission response. The optical responseat the excitation wavelength can be notch-filtered or otherwiseattenuated or removed from the optical response information, such as foremphasizing the fluorescent emission relative to the optical response atthe excitation wavelength. The multiple fluorescence emission bands(e.g., from Nicotinamide adenine dinucleotide (NADH), flavin adeninedinucleotide (FAD), collagen, elastin, a calcium-sensitive or voltagesensitive dye, as an illustrative example) can be spectrally separatedusing the dispersive element 146, and detected using a 2 dimensionallight detector array, or a series of stacked 1 dimensional linear lightdetector arrays, for example. In certain examples, information from the2D light detector array 148 can be used to measure light scattering intwo orthogonal directions (e.g., in an L-shape, rather than along aline). This may provide useful information about the tissue, such asinformation about the scattering anisotropy.

FIG. 2 is a schematic drawing illustrating generally an example of aninterface apparatus, such as for the system 100 illustrated in FIG. 1.In the illustrative example of FIG. 2, a housing 200 can be mounted ontoan articulated arm 202, such that the location of the housing 200 can bemanually, robotically, or automatically manipulated with respect to atarget object to be imaged, such as an external skin lesion 204 on apatient 206, for example. The housing 200 can house at least some of thecomponents illustrated in FIG. 1, such as the lens 114, the polarizingbeam splitter 116, the x-scanner galvanometer 124 the y-scannergalvanometer 126, the lens 128, and the lens 140. The optional objectivelens 208 can include the variable magnification lenses 134A-B of FIG. 1,such as in an example in which it is desirable to adjust the beam sizeupon the object, the field of view, or the effective separation betweenincident light and the detected optical response light. An optionalhollow tube 210 of a specified length (e.g., 150 mm) can be fitted tothe objective lens 208 or to the housing 200 to help provide andmaintain a consistent desired spacing between the objective lens and theobject to be imaged. The tube 210 can be at least partially opaque, suchas to the wavelengths of light used in the imaging, such as to helpprotect a user or subject from exposure to stray laser light, forexample. The tube 210 can be transparent to other portion(s) of thevisible spectrum, if desired, so as to allow the user to visualize thetarget 204. Spacing apart from the target tissue is not required. Inanother example, a distal portion of the apparatus is pressed directlyagainst the target tissue, which may help reduce motion artifact. Such amechanism can also include a safety interlock, in certain examples, suchas to inhibit or prevent accidental exposure to laser radiation. Adisposable (e.g., transparent) plastic barrier can be used so that theapparatus need not be cleaned between uses with different patients.

FIG. 3 is a diagram illustrating generally an example of a method 300that permits concurrently obtaining and separating depth-resolved andspectrally-resolved laminar optical tomography information, such as foruse in imaging or spectroscopy. At 302, light is sourced at two or moredifferent wavelengths, which can be either distinct individualwavelengths or a broader spectrum of wavelengths. For example, this caninclude incident light at 635 nm, 532 nm, and 473 nm, such asillustrated in FIG. 1. At 304, an incident beam location is scannedacross an imaging area of interest. For example, this can include usingan x-galvanometer and a y-galvanometer, such as described with respectto FIG. 1. At 306, an optical response to the incident light can bedetected at multiple locations, such as at different lateral distancesfrom the incident beam location being scanned at that particular time.At 308, the constituent wavelengths of the optical response aredispersed, such as across a linear dimension. This linear dimensionacross which these wavelengths are dispersed can be arranged to beorthogonal to a linear dimension of the different locations at which theincident light is detected at 306. At 310, the optical response to theincident light is detected across the different locations and across thedifferent wavelengths. For example, this can include using atwo-dimensional optical detector such that the different locations aredispersed across a first direction (e.g., an x-direction) and thedifferent wavelengths are dispersed across a second direction (e.g., ay-direction) that is orthogonal to the first direction. At 312, theresulting detected response data can be stored, such as in atwo-dimensional memory array with memory locations corresponding to thedifferent locations in the two-dimensional optical detector used at 310.As the incident beam is scanned across different scanning locations ofthe imaging region of interest, a two-dimensional array of response datacan be detected and stored for each such scanning location. The data canbe used for producing a rendered volumetric image, or for performingspectroscopy analysis (e.g., using the object's spectral absorption orfluorescence profile), such as to determine the volumetric compositionof the object.

Thus, in certain examples, the above system 100 and method 300 can use atwo-dimensional detector array, multiple linear detector arrays, ormultiple linear detectors, along with a diffraction grating, prism, orother spectrally separating optical element to concurrently imagemulti-spectral on-axis or off-axis scattered light from a scanning spotto allow depth-resolved optical imaging or spectroscopy. For example,the two-dimensional detector array is useful for performingmulti-spectral LOT imaging or spectroscopy. The linear array is usefulfor DCS. The above system 100 and method 300 are advantageous over asystem and method that uses serial illumination of different wavelengthsof laser light, and either multiple individual detectors or a lineararray of detectors. Serial illumination of different wavelengths oflight typically involves a complicated shuttering process. It willtherefore result in slower imaging frame rates, and can result in a lackof simultaneity in measurements of living dynamic systems (e.g.,movement artifacts or fast hemodynamic changes can inhibit quantitativespectroscopic analysis of results). Examples of some applications of thepresent systems and methods include, without limitation, fluorescence,absorption, or scattering contrast imaging or other spectroscopy ofliving tissues, such as the brain, retina, skin, or endothelial tissuessuch as the oral mucosa, colon, or cervix. By having concurrentlyacquired multi-spectral absorption or fluorescence measurements, rapidfunctional imaging can be accomplished. Multi-spectral detection allowsseparation of signals, such as from mixtures of fluorophores orchromophores, such as voltage or calcium sensitive dyes, molecularprobes, collagen, NADH, flavoproteins, tryptophan, oxyhemoglobin,deoxyhemoglobin, melanin, lipid, water, cytochrome, etc. For example,FIG. 4 is an example of a plot of absorption vs. wavelength for melanin,HbO₂, and HbR, demonstrating that the laser wavelengths described withrespect to FIG. 1 can provide measurements for achieving spectralseparation. As an illustrative example, if spectral information at threewavelengths is acquired, and spectral response information about threesubstances is known, this permits simultaneous solving of threeequations of three variables, such as to obtain information aboutconcentrations of the three substances. Thus, there are considerableadvantages to the ability of the present systems and methods toefficiently combine both multi-spectral and depth-resolved imaging orspectroscopy data, and the present systems and methods are not limitedto dermal imaging or spectroscopy, but can also be used in otherapplications such as, for example, brain imaging, or non-clinical ornon-biological applications.

FIG. 5 is a schematic drawing illustrating generally an example of asystem 500, such as for concurrently performing LOT and diffusecorrelation spectroscopy (DCS). As described above, LOT can beconfigured to concurrently provide both spectrally-resolved anddepth-resolved imaging or spectroscopy data, such as by scanning anincident light beam across a tissue or other region of interest, andusing optical response information such as absorption or fluorescence.The present inventor has also recognized that by concurrently performingDCS, blood flow or other useful information can also be obtained, suchas concurrently obtained along with the LOT data. This is useful, as anillustrative example, in a brain imaging application such as fordetermining whether ischemic is present, such as resulting from astroke, for example.

DCS generally involves using a laser source for providing incidentlight, such as at a wavelength that typically exhibits a desiredcoherence length over which the incident light maintains a desireddegree of coherence. Light scattering by the tissue or other targetobject can be detected. Fluctuations in the detected scattered light canbe ascertained, such as by using a correlator circuit or like module tocompute one or more temporal correlation statistics of the detectedscattered light. In tissue having blood flow, such as a region ofinterest of the brain, for example, less blood flow will result in alonger time-constant of temporal correlation of the detected scatteredlight. Conversely, more blood flow will result in a shortertime-constant of temporal correlation of the detected scattered light.Information about blood flow or changes in blood flow is useful byitself. Moreover, such information can also be used, for example, indetermining tissue oxygenation, tissue oxygen extraction, or tissueoxygen metabolism. DCS information can also be used to generate 3Dimaging information, such as described further below.

FIG. 5 is similar to FIG. 1 in certain respects. In the example of FIG.5, laser light sources 502, 504, and 506 are similar to the laser lightsources 102, 104, and 106 of FIG. 1. In the example of FIG. 5, the lightsource 502 emits laser light at a wavelength 636 nm, the light source504 emits laser light at a wavelength of 532 nm, and the light source506 emits laser light at a wavelength of 488 nm. This example alsoincludes a light source 507 that emits light having a desired coherencelength for performing DCS. In this example, the laser light source 507emits laser light at a wavelength of 800 nm, which can permit using thedesired coherence length for performing DCS.

In this example, the different wavelengths of light from thecorresponding different lasers 502, 504, 506, and 507 are combined anddelivered to the lens 104, either directly or such as via an optionaloptical fiber conduit 108. In certain examples, such as for providinglight for performing DCS, a single-mode low dispersion optical fiberconduit 108 is used. In this example, in which four differentwavelengths of light are shown for illustrative purposes, the combiningof the different wavelengths of light can be accomplished similarly tothat described above with respect to FIG. 1, but including an additionalfrequency selective filter (e.g., a 45° angled dichroic mirror 508). Thedichroic mirror 508 passes light having wavelengths longer than 700 nm(such as the 800 nm light from the laser 507) and reflects shorterwavelengths (such as the 636 nm light from the laser 502).

The light from the light sources 502, 504, 506, and 507 is delivered tothe optical fiber or other optical conduit 108 and, similarly to theabove description with respect to FIG. 1, is delivered to a site ofinterest 536 in an object of interest 538, such as a brain region, forexample. In the schematic drawing of FIG. 5, a mirror 530 is used inplace of the optical conduit 130 of FIG. 1, however, the optical conduit130 of FIG. 130 of FIG. 1 could be used in FIG. 5 instead of the mirror530, and vice-versa. FIG. 5 also includes a frequency selective filter532 (e.g., one or more 45° angled dichroic mirrors). The frequencyselective filter 532 passes light having the same wavelengths as theincident light lasers 502, 504, 506, and 507 (e.g., passes light atwavelengths of 636 nm, 532 nm, 488 nm, and 800 nm, in this example).However, the frequency selective filter 532 reflects light at otherwavelengths, such as the fluorescence components of the optical responseto these incident light wavelengths. In this way, the fluorescenceoptical response signal can be extracted and provided to a lightdetector 539. This can be carried out via a refractive element, forexample, such as a lens 541 that focuses the light on a desired regionof the light detector 539. In this example, the light detector 539includes an at least one-dimensional (1D) array of individual lightdetecting elements, such as a 1D photomultiplier array, and theresulting information can be provided to a signal processor circuit 560.This permits resolving the fluorescence signal from different laterallocations at the site 536 with respect to the location of the incidentlight beam. As discussed above, such different lateral locationsrepresent responses from light that has penetrated to different depthsof the object 538; responses obtained at more distant lateral locationsare presumed to have penetrated into the object 538 more deeply. Using alight propagation model, such information can be used to generate a 3Dvolumetric image representation of the fluorescence optical response.The absorption optical response can be detected using the light detector148, such as described above with respect to FIG. 1, with the resultinginformation provided to a signal processor circuit 560 to performdesired computation or analysis. The signal processor circuit 560 cancommunicate with a user interface 562, which can include a display 564,such as for displaying rendered or other imaging information,spectroscopy information, or the like.

FIG. 5 also includes another wavelength selective optical filter (e.g.,a 45° angled dichroic mirror 540). In this example, the dichroic mirror540 passes light having wavelengths shorter than 750 nm and reflectslight having longer wavelengths. In this way, the optical response tothe 800 nm DCS laser 507 can be extracted from the second path 120 andreflected toward DCS detection components. In this example, such DCSdetection components can include a refractive element, such as a lens542, which focuses the light toward a light detector. In certainexamples, such as for DCS, the light detector is capable of countingreceived photons, such as to provide a resulting signal having anintensity that is a function of the photon count, or a resulting signalproviding a pulse per photon, or the like. In this example, such a lightdetector includes individual photomultipliers or an at least 1D (e.g.,1×8) photomultiplier array 544, however, the light detector couldinclude a pigtail of fibers or multiple individual light detectors. Inthe 1D array example, different locations along the 1D light detectorarray 544 receive an optical response signal from locations of thetarget that are different distances away from the incident light beam'slocation at the target. As described above, this provides informationabout light that has penetrated to different depths within the target;optical responses obtained at distances that are farther from theincident light beam location are presumed to be responses from lightthat has penetrated more deeply into the target object 538. In thisexample, each light detector in the 1D light detector array 544 providesinformation about its detected light to a correlator 546 circuit. Thecorrelator 546 computes one or more temporal correlation statistics thatcan be provided to the signal processor circuit 560 to perform DCS.Among other things, such DCS is useful for obtaining blood flowinformation. An example of obtaining blood flow information from DCS isdescribed in Joseph P. Culver et al., “Diffuse Optical Tomography ofCerebral Blood Flow, Oxygenation, and Metabolism in Rat During FocalIschemia,” Journal of Cerebral Blood Flow & Metabolism, 23:911-924,2003. Detected diffuse light intensity I(r,t) can be detected as afunction of distance, r, and time, t. A normalized intensityautocorrelation function of the diffuse light intensity can be computed.This can be used to calculate the diffuse electric field temporalautocorrelation function, which satisfies the correlation diffusionequation. The correlation function decay depends on a constant, k, whichcan be represented as:k ²=3μ_(s)′μ_(a)+6μ_(s)′² k _(o) ²Γτ  (1)where τ represents the autocorrelation time delay and k_(o) representsthe photon wavenumber in the medium. The parameter Γ=α_(B) characterizesblood flow; α represents the probability that a photon is scattered by amoving “cell” and is presumed proportional to cerebral blood volume. Theblood flow speed can be parameterized by a Brownian diffusion constant,D_(B), such as described in Culver et al. and the references citedtherein.

As described above, the DCS information can be used to obtain a rendered3D image that includes information about any changes in the blood flowthrough the tissue. Moreover, blood flow information can also be used,for example, in determining and displaying a 3D representation of tissueoxygenation, tissue oxygen extraction, or tissue oxygen metabolism. TheDCS-derived information is particularly useful in conjunction with theabsorption or fluorescence spectroscopic information provided by the LOTconcurrent to the DCS information generation.

Moreover, the present DCS configuration, which cleverly uses the x-yscanning from the LOT configuration of FIG. 1, is extremely useful overa DCS system that does not make use of such scanning, but that insteadwould acquire DCS data either by delivering light to and from tissueusing single mode optical fibers, or by using free-space lenses to imagea static grid of light sources and light detectors onto the surface ofthe tissue or other target being imaged. Both would result in lowresolution images, with very slow frame rates, since an optical switchwould be used to sequentially illuminates the source fibers in theircoarse pattern. Moreover, many parallel detection units would be neededto acquire the scattered light, thereby restricting the performance ofsuch a system. By contrast, by using the present x-y scanning, higherresolution, faster, and lower cost DCS information can be obtained—evenwithout using the components of FIG. 5 providing LOT absorption andfluorescence contrast information, if desired.

For example, if only DCS information is desired, components 502, 504,506, 110, 112, 532, 541, 539, 540, 140, 142, 144, 146, 152, and 148 canbe omitted; such an example can still take advantage of the presentscanning techniques in conjunction with DCS. If DCS and LOT fluorescenceinformation is desired, components 532, 541, 539 can be added back in,along with at least one of components 502, 504, or 506 and a respectiveat least one of components 508, 110, or 112. If DCS and LOT absorptioninformation is desired, components 540, 140, 142, 144, 146, 152, and 148can be added back in, along with along with at least one of components502, 504, or 506 and a respective at least one of components 508, 110,or 112. Multi-wavelength LOT absorption information can be obtainedusing the DCS laser 507 for providing at least one of the multiplewavelengths, if desired. In another example, if LOT absorption andfluorescence information is desired, but DCS information is not desired,the configuration of FIG. 5 can be modified to omit components 540, 542,544, and 546A-H.

Combining DCS with LOT presents certain technical challenges that thepresent approach has overcome, such as, for example, how to extract thedistinct wavelengths useful for DCS from other wavelengths useful forLOT, and how to perform the different DCS and LOT processingconcurrently—particularly where the LOT information can be bothspatially-resolved and spectrally-resolved, such as described above withrespect to FIG. 1. However, combining DCS with LOT is also useful in anexample that does not use a dispersive element 146 to obtainspectrally-resolved and spatially-resolved LOT, but which merelycombines spatially-resolved LOT with DCS.

Among other things, the combined LOT/DCS system illustrated in FIG. 5 iscapable of concurrently quantifying (1) absorption (and henceoxyhemoglobin and deoxyhemoglobin dynamics in living tissue), (2)fluorescence (such as that from a calcium sensitive or voltage sensitivedye, a targeted molecular probe, or an intrinsic fluorophore such asFAD, NADH, or collagen), and (3) blood flow via DCS.

Although FIG. 5 illustrates separate detection “pathways” for each offluorescence (e.g., via components 532, 541, and 539), absorption (e.g.,via components 140, 142, 144, 146, 152, and 148), and DCS (e.g., viacomponents 540, 542, 544, and 546), this is merely one convenientimplementation configuration. In other examples, it is possible to sharecomponents and, therefore, reduce the number of components used toimplement the system. For example, the 2D light detector array 148 neednot only be used to obtain the LOT absorption response information.Instead, the 2D light detector array 148 can also be used to performlight detection for obtaining the LOT fluorescence information, forobtaining the DCS information, or for obtaining both LOT fluorescenceinformation and DCS information.

For example, to use the 2D light detector array 148 to obtain the DCSinformation, the correlators 546A-H can be connected to elements in thelight detector array 148 that detect the particular wavelength desiredfor DCS (e.g., 800 nm, in this example). As described above with respectto FIG. 1, the dispersive element 146 is configured to disperse opticalresponse wavelengths along a first dimension of the 2D array, with theperpendicular second dimension of the array representing differentlateral optical response locations with respect to incident beamlocation. Thus, if a particular “row” of the 2D array represents 800 nmoptical response at different locations, then the correlators 546 can beindividually connected to the light detector elements in that row forobtaining the DCS information. Similarly, if a particular “column” ofthe 2D array represents 800 nm optical response at different locations,then the correlators 546 can be individually connected to the lightdetector elements in that column for obtaining the DCS information.Using the 2D light detector array 148 for obtaining LOT absorption andDCS information would allow components 540, 542, and 544 to be omitted.

In another example, the 2D light detector array 148 can be used toobtain the LOT fluorescence response, as well as the LOT absorptionresponse. Since fluorescence response occurs at wavelengths that aredifferent from the wavelength(s) of the incident light, the fluorescenceresponse information can be obtained from the 2D light detector array148 by ignoring information from those elements that are associated withincident wavelengths. For example, if the incident wavelengths used are800 nm and 636 nm, which, as the result of the dispersive element 146correspond to particular “rows” of the 2D light detector array 148, thenthe fluorescence response information can be obtained from other rows ofthe 2D light detector array 148. Similarly, if the incident wavelengthsused are 800 nm and 636 nm, which, as the result of the dispersiveelement 146 correspond to particular “columns” of the 2D light detectorarray 148, then the fluorescence response information can be obtainedfrom other columns of the 2D light detector array 148. In anotherexample, if the incident wavelengths used are 800 nm, 636 nm, 532 nm,and 488 nm, which, as the result of the dispersive element 146correspond to particular “rows” of the 2D light detector array 148, thenthe fluorescence response information can be obtained from other rows ofthe 2D light detector array 148. Similarly, if the incident wavelengthsused are 800 nm, 636 nm, 532 nm, and 488 nm, which, as the result of thedispersive element 146 correspond to particular “columns” of the 2Dlight detector array 148, then the fluorescence response information canbe obtained from other columns of the 2D light detector array 148. Usingthe 2D light detector array for obtaining LOT absorption and LOTfluorescence information would allow components 532, 541, and 539 to beomitted. Using the 2D light detector array for obtaining LOT absorption,LOT fluorescence, and DCS information would allow components 540, 542,544, 532, 541, and 539 to be omitted.

Although certain examples have been discussed in terms of using a 2Dlight detector array, multiple 1D light detector arrays could be“stacked” or otherwise used, or a combination of 1D and 2D lightdetector arrays could be used. This will allow mixing or matching ofdifferent detector arrays having different properties, as desired.

FIG. 6 is a diagram illustrating generally an example of portions of amethod 600, which can be performed at least in part by using the systemof FIG. 5, if desired. At 602, light of at least one wavelength issourced to form an incident beam. The light generally will include lightthat has a desired coherence length, such as described above. In certainexamples, light of multiple distinct different wavelengths can beprovided, such as described above. At 604, the incident beam is scannedacross a target region. In certain examples, from this same scanninginstance, both DCS and LOT information is obtained, such as describedabove. At 606, in response to the scanning and for a particular beamlocation, a scanning optical response signal is obtained. In certainexamples, the optical response signal for a particular beam location isobtained at multiple different locations (e.g., different distances)from the incident beam location. In certain examples, the opticalresponse signal includes multiple wavelengths, such as for LOTabsorption spectroscopy, for example. In certain examples, the opticalresponse signal includes one or more wavelengths that are different fromthe one or more incident wavelengths, such as for LOT fluorescencespectroscopy, for example. In certain examples, the optical responsesignal includes a DCS wavelength that attains at least a particulardesired coherence length. At 608, a temporal correlation is computed,such as described above. In certain examples, a temporal correlation iscomputed for the optical response signal corresponding to each of themultiple different locations (e.g., different distances) from theincident beam location. At 610, a characteristic of the target region iscomputed using the temporal correlation information. In certainexamples, this includes computing one or more of a blood flowcharacteristic, a tissue oxygenation characteristic, an oxygenmetabolism characteristic, or forming or displaying a rendered 3Drepresentation of one or more of such characteristics.

The present inventors have also recognized that using an at leastpartially flexible optical conduit 130, such as shown in FIG. 1, will incertain situations provide advantages over an example that does not usesuch an at least partially flexible optical conduit 130, such as theexample of FIG. 5 that instead uses a mirror 530, which can be replacedby the optical conduit 130. In certain examples, the at least partiallyflexible optical conduit 130 can be used to provide a tethered handheldwand for external imaging or spectroscopy. In certain other examples,the at least partially flexible optical conduit can be used to provide alaparoscopic or endoscopic probe such as for carrying outminimally-invasive or other internal diagnostic or prognostic imaging orspectroscopy. For example, this can permit the above-described LOT andDCS techniques to be performed on the oral mucosa, cervix, esophagus,colon, trachea, lung, etc., or performed during surgery, such as byembodying the flexible optical conduit 130 within an at least partiallyflexible and externally steerable endoscope (such as a colonoscope, forexample), which can include flexible and steerable viewing optics.

FIG. 7 is a cross-sectional schematic drawing illustrating generally anexample of a distal portion 700 of an externally steerable laparoscopeor endoscope that includes an optical conduit 130, which in someexamples can be at least partially flexible, such as for a laparoscopicor endoscopic LOT, DCS, or other procedure, such as discussed above, tobe carried out within a body such as within a body lumen. In certainsuch applications, it is desirable to obtain a 360 degree or othercircumferential image about an interior of the body lumen, such as byusing a longitudinal-to-circumferential optical translator guide. In theexample of FIG. 7, a rotatable angled mirror 702 or prism can bepositioned at the distal portion 700 with respect to the optical conduit130. In the example shown, a rotatable 45° angled mirror 702 canredirect the incident light beam from along a longitudinal axis of theoptical conduit 130 through a transparent (e.g., at the operativewavelengths) window 706 toward a circumferential site 704 on theinterior of the body lumen into which the distal portion 700 isinserted. This provides a “side-looking” elongated apparatus. However,the mirror angle can be established or adjusted, such as to additionallyor alternatively provide rearward or forward imaging. In this example,the mirror 702 can similarly redirect the optical response from thecircumferential site 704 back along the longitudinal axis of the opticalconduit 130, such as toward a proximal external location for performinglight detection and signal processing, such as described above. Themirror 702 can be rotated about the longitudinal axis of the opticalconduit 130, such as to provide full 360° degree imaging orspectroscopy, if desired. In the example of FIG. 7, an outer cylinder708 with an atraumatic blunt head 710 rotates about the optical conduit130. A distal portion of the outer cylinder 708 carries the mirror 702and includes the window 706, such that rotation of the outer cylinder708 rotates the mirror 702 and the window 706, such as to enablecircumferential imaging or spectroscopy. Other techniques may also besuitable for rotating the mirror 702 or otherwise providingcircumferential viewing, imaging, or spectroscopy. A dichroic mirror 702can also be used, for example, to pass at least one different wavelengthof light along the longitudinal axis of the optical conduit 130 throughthe mirror 702 and through an optically transparent head portion 710 (orto another differently-oriented angled mirror). This can provide viewingalong the longitudinal axis of the optical conduit 130, which can behelpful for viewing or guiding the distal portion 700 within the bodylumen, or even for providing LOT, DCS, or other like capability alongthe longitudinal axis of the optical conduit 130. In the example of FIG.7, the variable magnifier 132 can be located at the distal end of theoptical conduit 130, near the mirror 702, or at the proximal end of theoptical conduit 130.

In certain applications, it can be desirable to fixate the distancebetween the optical conduit or variable magnifier 132 and the site 704.In certain examples, this can be accomplished by using a transparentwindow 706 having the desired thickness to maintain the desiredseparation. In certain examples, this can be accomplished by using atoroidal or other balloon cuff 712 located circumferentially about thedistal portion 700. The toroidal balloon cuff 712 can be remotelyinflatable, such as via a fluid conduit 714 that extends toward aproximal external end of the endoscopic or laparoscopic apparatus. Incertain examples, the desired separation can be maintained by aplurality of arms that can be remotely actuated to splay outward orretract inward. Other techniques can also be suitable for maintainingthe desired separation.

In certain examples, the side-looking distal end of FIG. 7 usesproximal-end x-y scanning, such provided by the scanner 122 of FIG. 1.However, it may be possible to obtain the desired information withoutsuch scanning. For example, movement of the endoscope or laparoscope(e.g., insertion, withdrawal, or rotation) can be used to control thelocation at which incident light is delivered, or the location where anoptical response is obtained. In another example, movement of an element(e.g., mirror 702) within the endoscope or laparoscope (e.g., rotation,telescopic or other extension or retraction) can similarly be used tocontrol the location at which incident light is delivered, or thelocation where an optical response is obtained.

FIGS. 8A, 8B, and 8C provide a schematic example of a side-lookingendoscopic or laparoscopic probe for performing optical tomography suchas for imaging or spectroscopy. FIG. 8A shows a generally tubular bodyorgan 800, such as a colon, blood vessel, or the like. Within theorifice 802, a longitudinal-to-side optical translator guide, such as arotatable mirror 804 or prism, can re-direct light from along alongitudinal axis and toward a region of interest 806 on and within theinterior wall of the orifice 802. FIG. 8B shows the rotatable mirror804, with a linear arrangement of optical fibers 808A-G. In thisexample, the fiber 808A provides incident light to the tissue via themirror 804. The fibers 808B-G measure the optical response, via themirror 804, at various lateral distances from the location of theincident light provided by the fiber 808A. In certain examples, one ormore of the fibers 808 includes a lens at its distal end, such as agraded refractive index (GRIN) lens, such as for focusing the incidentlight upon the mirror 804, or for collecting the optical response lightfrom the mirror 804. FIG. 8C shows a side view.

In an example, the mirror 804 rotates together with the lineararrangement of fibers 808—this can be accomplished by rotating theendoscopic apparatus carrying these elements, or by providing rotationof these elements within the endoscopic apparatus carrying theseelements. Such rotation permits 360-degree circumferential imaging orspectroscopy within the orifice 802. A back-and-forth rotation can alsobe used, e.g., a 360-degree rotation in one direction, followed by a360-degree rotation in the opposite direction. The mirror 804 can alsobe inserted deeper into the orifice 802 or retracted outward from theorifice 802, together with or independent from the circumferentialrotation. This can be accomplished by moving the endoscopic apparatuscarrying these elements, or by providing telescopic extension orretraction of these elements within the endoscopic apparatus carryingthese elements, or other desired element, such as, for example, a MEMsmirror array to steer the light.

Although the above description has emphasized examples in which light isincident substantially perpendicular to region of interest, the presentinventors have also recognized that providing the incident light at anon-orthogonal angle to the region of interest can actually bedesirable, and has the potential for providing higher sensitivity andbetter imaging or spectroscopic resolution. Without being bound bytheory, this increased depth sensitivity is believed to be particularlyeffective at shallow depths, where there is a significant degree ofdirectionality of the light within the tissue. An intersection pointbetween incident light and detected light pathways will providelocations of highest sensitivity for imaging or spectroscopy. In someexamples, detection can be performed at an oblique angle andillumination can be performed at a perpendicular angle.

FIG. 9 is a schematic drawing showing an example in which incident light900 is provided through a lens 902 to a polarizing beam splitter 904that passes S polarization and reflects P polarization toward a mirror906. The mirror 906 reflects the light with P polarization toward aregion of interest 908, where it is incident at a non-perpendicularangle to the region of interest, such as at the angle 910 measured froma line that is perpendicular to the region of interest 908. Thescattered incident light will lose its polarization as it is scatteredwithin the tissue of the region of interest 908, and specular reflectedlight will maintain its P polarization, but such optical response willbe rejected upon return to the polarizing beam splitter 904 from theregion of interest 908. FIG. 9 also shows optical response detectionpathways 912A-C spaced at various lateral distances from the location ofthe incident light. The optical response returns along the pathways912A-C through a lens 914 to the polarizing beam splitter 904, whichpasses light with S polarization on to the lens 902, and to a lightdetector, such as described above in the other examples. The angledincident beam 906 provides regions of increased sensitivity at theintersections with the optical response return pathways 912A-C, beyondthat which could be obtained if the incident light were perpendicular tothe target region 908 and laterally spaced from the optical responsereturn pathways 912A-C. The lens 902 can be used to account for thedifference in path length of the light diverted by the polarizing beamsplitter 904.

The particular angle of incidence 910 can take on any desired value inthe range of 0 degrees and 90 degrees. In an example, the angle 910 isbetween 10 degrees and 80 degrees. In another example, the angle 910 isbetween 20 degrees and 80 degrees. In another example, the angle 910 isbetween 10 degrees and 50 degrees. FIGS. 10A-10G are color plots ofmodeled simulation data illustrating sensitivity functions indicatingthe most probable paths of the light, with red indicating a largerprobability through that particular region, and blue indicating asmaller probability through that particular region. Informationdetection will be more sensitive in the areas in which there is a largerprobability of the light having passed through. In each of FIGS.10A-10G, the incident light enters the tissue surface, at 1000, at anangle 910 that is 15 degrees from a line perpendicular to the tissuesurface. The optical response is measured at 1002 in an orientation thatis perpendicular to the tissue surface. The separation distances betweenthe incident location 1000 and response location 1002 are 3.00 mm (FIG.10A), 2.50 mm (FIG. 10B), 2.00 mm (FIG. 10C), 1.00 mm (FIG. 10D), 0.5 mm(FIG. 10E), 0.2 mm (FIG. 10F), and 0.00 mm (FIG. 10G), respectively. Asseen in FIGS. 10A-G, it is possible to tailor the separation distanceand the incident angle to select a desired region, to provide increasedsensitivity at that desired region, if desired. The angle at which theoptical response is detected could also be adjusted, if desired. FIGS.10A-G also show that, in general, shorter lateral separation distancesbetween incident and response locations are more sensitive to shallowerregions, and wider lateral separation distances between incident andresponse locations are more sensitive to deeper regions.

FIGS. 11A-11G are similar color plots illustrating sensitivityfunctions, for a 35-degree incident angle 910, and separation distancesof 4.00 mm (FIG. 11A), 3.00 mm (FIG. 11B), 2.00 mm (FIG. 11C), 1.50 mm(FIG. 11D), 1.00 mm (FIG. 11E), 0.40 mm (FIG. 11F), and 0.00 mm (FIG.11G). As seen in FIGS. 11A-G, it is possible to tailor the separationdistance and the incident angle to select a desired region to provideincreased sensitivity at that desired region, if desired. The angle atwhich the optical response is detected could also be adjusted, ifdesired.

In some examples, Monte Carlo simulation can be used to form areconstruction model that can be used to create the plots of FIGS. 10A-Gand 11A-G, respectively. The reconstruction model can also be used toreconstruct an image from the acquired optical response data, ifdesired. A sensitivity function (such as illustrated in the plots ofFIGS. 10A-G and 11A-G) can be defined as:J _(n,m)(r)=δM _(n,m)/δμ_(a)(r).  (2)

In Equation 2, above, for a given incident light location, n, and agiven optical response detection location, m, the sensitivity functionJ_(n,m)(r) will be a function of the position r within the tissue.M_(n,m) represents a measurement at the tissue surface. μ_(a)(r) is theabsorption at the position r within the tissue. δM_(n,m) represents achange in the measurement M_(n,m). δμ_(a)(r) represents a change inμ_(a)(r). Equation 2 uses the Born approximation, which assumes a linearmodel relating M_(n,m) and μ_(a)(r). The Born approximation assumes thatδμ_(a)(r) is small, so that J_(n,m)(r) can be used to predict M_(n,m).Alternatively, the Rytov approximation can be used, which replacesδμ_(a)(r) with exp(δμ_(a)(r)). However, the real relationship relatingM_(n,m) and μ_(a)(r) is non-linear. Therefore, for larger absorptionchanges, δμ_(a)(r), or for other reasons, it may be desirable to use anon-linear reconstruction that updates estimates of J_(n,m)(r) based onthe structure of the target object.

From Equation 2, if a modeled sensitivity function J_(n,m)(r) is known,then the absorption μ_(a)(r) at various positions within the tissue canbe calculated from the measured δM_(n,m) Monte Carlo simulation can beused to calculate the modeled sensitivity function J_(n,m)(r). At depthsinto the tissue that are shorter than the mean scattering length oflight in the tissue, directionality of the incident light can beimportant. Therefore, at such distances into a tissue sample,information about the angles of propagation of the photons can beincluded in the model. At distances into the tissue that exceed the meanscattering length of the light in tissue, a diffusion approximation tothe equation of radiative transport can optionally be used in the model.The radiative transport equation itself can be used in the model, ifdesired. Moreover, instead of Monte Carlo simulation, empiricalmeasurements or other modeling (e.g., finite element modeling (FEM),finite difference modeling, Maxwell's equations, or the like) can beused to create the reconstruction model.

The reconstruction model can also incorporate any information knownabout the target object. For example, such known information can beincorporated into the model as one or more constraints upon the model,or as constraints upon 3D or other image reconstruction or spectroscopicinformation obtained using the model. In an example, if a particulartype of target tissue is known, then the model can incorporateinformation about that particular target tissue type. For example, braintissue exhibits less light scattering than skin tissue. Therefore,information about the lower scattering of brain tissue can beincorporated into the model. Darker skin exhibits more light absorptionthan lighter colored skin; this information about a known target can beincorporated into the model. Also, the model can also incorporatespectral information about the particular chromophores expected in thattype of target tissue. Similarly, known information about target shapecan be used to generate the model. Likewise, information about theparticular wavelength of incident light can be incorporated into themodel. In certain examples, it is not necessary to actually create a 3Dimage using the model. Instead, raw data can be processed or presentedto a user without actually creating a 3D image. In an example, one canalso use a non-linear model that need not require a linearizationassumption like Born or Ryton. A look-up table approach could also beused, in an example. In an example, pixel-by-pixel analysis of opticalproperties and shape functions can be performed without performing acomplete image reconstruction.

Although the above description has emphasized an example in whichabsorption due to light scattering is modeled, a target's fluorescenceresponse can be similarly modeled. Fluorescence results from a photonbeing absorbed by a fluorophore and a different photon (of longerwavelength) being emitted. Therefore, the amount of fluorescence lightemitted will depend on the absorption coefficient of the fluorophore,the quantum yield of the fluorophore (how many incident photons aregenerally required to trigger the fluorescent emission of a photon), andthe concentration of the fluorophore in the target sample of interest.Therefore, fluorescence can be modeled by replacing μ_(a)(r) in Equation2 with a μ_(af)(r) term denoting fluorescence absorption. Other lesssimplified models can also be used. For example, because in fluorescencethe absorbed photon is of shorter wavelength than the emitted photon,the incoming and emitted photons experience different absorption andscattering, and such differences can be included in the model. Thedirectionality of the incident light is important in modeling scatteringevents until a fluorophore is encountered, however, since fluorescenceemission is generally random in direction, this can also be incorporatedinto the model. In another example, a combined model of bothfluorescence and absorption can also be used, such as to account forinteraction between the fluorescence response and the absorptionresponse of a target region of interest. In an example, Raman scatteringor other optical contrast can be examined.

Articulating Arm Example

As described above, LOT can allow non-contact depth-resolved opticalimaging, such as for example of living tissues to depths even greaterthan 2 millimeters with on the order of about 100 to 200 micrometerresolution, and with sensitivity to both absorption and fluorescencecontrast. In certain examples, LOT can use a beam of light that isscanned over the surface of the tissue, such as by using galvanometermirrors, such as described above. In response to the scanning beam,light can be detected, such as from areas adjacent to the location ofscanning beam upon the target. The further away from the incident beamlocation that the light has traveled, the deeper that it has traveledinto the tissue, and this can thereby be used to provide depth sensitivemeasurements. Using a model-based reconstruction algorithm, this datacan be reconstructed into depth-resolved images of optical contrast, incertain examples, such as described above.

The present inventors have recognized, among other things, that LOT orDCS data can be more conveniently acquired (such as in a clinicalsetting) using an articulating arm, such as for communicating light toor from the target location, such as the surface of a person's body orany other desired target location. Such an articulating arm can providethree pivots (e.g., correspondingly providing three axes of rotation),which can advantageously be used to allow LOT or DCS techniques to beperformed at any desired location on the external surface of the body,for example. Moreover, one or more additional pivots can be furtheradded, such as to further increase the degrees of freedom (e.g., bycorrespondingly providing further axes of rotation, if desired). Incertain examples, the articulating arm setup can be used to allow LOT orDCS techniques to be performed during surgery, such as to helpdistinguish diseased tissue from normal tissue, for example. In certainexamples, the articulating arm setup can be combined with the endoscopicarrangement, such as described above.

The sensitivity of LOT to oxygenation contrast and to both intrinsic(e.g., collagen, NADH, flavoproteins, tryptophan and oxy- anddeoxy-hemoglobin, melanin, lipid, water, cytochrome etc.) and exogenouscontrast (e.g. voltage, calcium or pH sensitive dyes, molecular probes),as well as the above-described LOT example providing parallelizedmulti-spectral detection (sometimes referred to by the present inventorsas “SpectraLOT”) can produce a highly versatile and relativelyinexpensive medical imaging modality with particular suitability toclinical imaging applications, particularly when used with thearticulating arm, endoscopic apparatus, or both.

A LOT or DCS system using the articulating arm can be configured invarious ways. For example, FIG. 2 shows an illustrative example in whicha housing 200 with various optical components is mounted on anarticulating arm 202. However, in an example, such as shown in FIG. 2,in which the articulating arm 202 does not provide for opticalcommunication through the articulating arm 202 (e.g., using a separateoptical fiber conduit 108), a bulky housing 200 at the distal end of thearticulating arm 202 could be needed in order to house the variousoptical components as shown in FIG. 2. In an example, the articulatingarm 202 can include one or more springs, one or more counter-weights, orrobotic control, such as for stability or positioning.

FIG. 12 shows an example of an articulating arm 1200 that can provideoptical communication along and within the articulating arm 1200 itself.This allows the optical components to be located at a proximal end ofthe articulating arm 1200, such that any such bulky optical componentscan be more conveniently housed away from the subject or object to whichLOT or DCS is being applied. In an illustrative example, the housing 200of FIG. 2 can omit the articulating arm 202. Instead, the housing 200can be located at proximal end (away from the subject 1202) of thearticulating arm 1200. In an example, the articulating arm 1200 caninclude pivots 1204A-C. Each of the pivots 1204A-C can include or becoupled to a respective cylindrical or other elongated or other segment1206, along which light can be longitudinally communicated, and anangled (e.g., 45 degree) mirror 1208, to redirect light in aperpendicular direction thereto. The cylindrical segments 1206 can beconfigured to pivot or rotate about their respective longitudinal axes,such that the combination of the pivoting or rotating segments 1206 andthe angled mirrors 1208 provide an adjustable articulating arm 1200 thatcan communicate light therewithin (e.g., without requiring an opticalfiber transmission medium). In an illustrative example, the pivot 1204Acan be mounted, in place of the spacer tube 210, to the housing 200. Inthis way, light for LOT or DCS can be provided via the objective lens208 into the pivot 1204A, in which it can be perpendicularly redirectedby the angled mirror 1208A into the rotatable cylindrical segment 1206A.Then, such light can pass through the segment 1206A into the pivot1204B, in which it can be perpendicularly redirected by the angledmirror 1208B into the rotatable cylindrical segment 1206B. Such light,in turn, can pass through the segment 1206B into the pivot 1204C, inwhich it can be perpendicularly be redirected by the angled mirror 1208Cinto the last cylindrical segment 1206C (which can, but need not, bepivotable or rotatable). Light from the last segment 1206C is directedonto the subject 1200. The return optical signal can traverse a reversepath along the articulating arm 1200.

FIG. 13 shows a schematic illustration of components of the articulatingarm 1200 used in conjunction with LOT components, such as alreadydescribed in detail above with respect to FIGS. 1, 2, and 12. Thesegments 1206 can include respective refractive elements, such asrefractive lens 1210, as desired. Thus, FIG. 13 shows an illustrativeexample of the articulating arm 1200 coupling the laser scanning beam tothe patient 1200. In the example of FIG. 13, the galvanometer mirrors ofthe galvanometer 122 provide x and y scanning of the incident beam.Mirrors 1208 located at the pivot joints 1204 of the articulating arm1200 are positioned so as to perpendicularly redirect the scanning beam,ultimately toward the image plane. The field of view or source-detectorseparation distances can be adjusted, in certain examples, such as bychanging the ratio of the focal lengths of the scan lens 208 anddetector lenses 140, 144, and 152.

FIG. 14 shows a schematic illustration of how the lenses 144 and 152 andthe diffraction grating or other wavelength dispersive element 146 canbe used to spectrally separate the response signal in the z-direction ofthe two-dimensional light detector array 148, with spatial separation ofthe optical response signal being orthogonal thereto, such as in they-direction as shown in FIG. 14.

Example of Simultaneous Multi-Wavelength LOT Imaging of Skin Cancer

Lentigo maligna (LM) is a lesion in the skin's epidermis. LM mostlyoccurs in older individuals, such as on sun-damaged skin of the head andneck. The lesions typically appear as a dark brown to tan discolorationon the skin. The lesion boundaries and depth of invasion are difficultto determine. Such information can be very important for propertreatment. Upon extension of the invasion from the epidermis into thedermis, LM is referred to as lentigo maligna melanoma (LMM). Theprognosis for LMM is worse than for LM because the dermis contains bothvascular and lymphatic networks, thereby providing a metastaticpotential. A treatment for LM and LMM is surgical excision of thetumor-containing tissue. Since the lesions typically occur on the faceand neck, the surgery has an additional complexity to fully remove thetumor-containing tissue while preserving facial features. At the presenttime, it is uncertain whether LM will provide good contrast, because(without being bound by theory) the edges are believed not usually highin melanin. However, it is believed that other dermatology applicationscan also benefit from the present systems and methods.

FIG. 15 shows an example of a cross sectional schematic view of skinimaging, such as with respect to skin that, in this example, includes anepidermis layer extending from the surface to a depth of about 100 μmbelow the surface, a cutis layer beginning at about 2000 μm below thesurface, and a dermis layer located between the epidermis and the cutislayers. In this example, a focused laser beam can be scanned over theskin surface, such as at the location of a lesion. Light remitted atlocations further from that of the incident laser beam providesinformation about deeper subsurface (e.g., at z1, z2, z3) opticalproperties of the tissue. LOT can be used for imaging skin lesions. Asdescribed above, LOT can provide a non-contact imaging system capable ofdepth-resolved imaging, such as, for example, to depths of up to about 2mm with up to about 100-200 μm resolution at up to about 100 frames persecond. LOT can scan a focused laser beam over tissue and measure thescattered light emerging at successive lateral distances of up to 2.5 mmaway from the scanning location, such as shown in the example of FIG.15. The response light measured at further distances from the focusedincident scanning spot can reveal respectively deeper subsurfaceabsorption and fluorescence properties of the tissue. For example, LOTcan be used to measure the depth-resolved absorption properties ofmelanin, oxyhemoglobin, or deoxyhemoglobin.

Melanocytes, the pigment (melanin) producing cells in the epidermis, arethe cells that become cancerous in malignant melanomas. At present, thediscoloration associated with an increased concentration of melanin isgenerally the surgeon's primary way of determining surgical margins ofLM. However, in some cases, the true margins of LM extend beyond thearea of pigmentation visible from the surface. This can lead tore-excisions or recurrence of the disease.

Dermal vascularity is expected to significantly increase beneath in situLMM, such as compared with normal skin or when LM is present withoutdermal invasion, in which cases the vascularity is believed less likelyto significantly differ from surrounding skin. Therefore, LOT's abilityto measure the amount, and oxygenation state of blood beneath a lesioncan be useful for surgical staging or further treatment planning.

While LOT can be used for studying hemodynamics, such as in the exposedrodent brain, it can also be configured for clinical use. By way ofexample, but not by way of limitation, it can be used to acquiresimultaneous three-wavelength measurements of skin. Among the benefitsof making multi-wavelength spectroscopic measurements simultaneously arethat doing so allows very rapid acquisition, and precise spectroscopy ofskin chromophores. If images of three wavelengths were acquiredsequentially, there would be significant risk of the patient moving,which would prevent accurate pixel-by-pixel analysis of the resultingdata. LOT can provide the surgeon with a tool to help pre-surgicalplanning. LOT can be used to measure the depth of invasion and toprovide measurements that allow the surgeon to better delineate thetumor boundaries. By simultaneously scanning and measuring 3 wavelengthsof light, LOT could provide accurate measurements of subsurface melanin,oxy-hemoglobin (HbO) concentration, or deoxy-hemoglobin (HbR)concentration. Such measurements could help enable more preciseexcisions around the tumor-containing tissue, thereby minimizing theamount of tissue removed, such as near important facial features.

FIG. 16 shows a schematic drawing of an example of a LOT system 1600that can include multiple (three, in this example) lasers, such as thelaser 106 (e.g., 85-BCD-030-115, Melles Griot) providing light ofwavelength of 488 nm, the laser 104 (e.g., 85-GCA-020, Melles Griot)providing light of wavelength of 532 nm, and the laser 102 (e.g.,56RCS004/HS, Melles Griot) providing a light of a wavelength of 638 nm.Light from the lasers 102, 104, and 106 can be collinearly aligned intoa single polarization maintaining single mode fiber 108. The resultingmulti-wavelength beam can then be emitted from the other end of thefiber 108, collimated (e.g., using the lens 114) and passed through apolarizing beam splitter 116 cube and a 3-line dichroic filter 1602before being reflected by an x-scanning mirror 124 and a y-scanningmirror 126 of a galvanometer 122. The galvanometer mirrors 124, 126 canscan the beam through an f=30 mm scan lens 128 before passing through a1× objective or other lens 134 and onto the tissue 1604.

While the multi-wavelength incident beam is scanned over the region ofinterest, scattered light emerging from the tissue travels back throughthe objective lens 134, through the scan lens 128 and onto thegalvanometer mirrors 124, 126. The mirrors 124, 126 de-scan the remittedlight, directing it back towards the dichroic 1602 and the polarizingbeam splitter 116 cube. Fluorescent response light (at wavelengthsdifferent from that of the incident light) can be redirected by thedichroic 1602 to a fluorescence light detector, such as the 1×16photomultiplier tube (PMT) array 1606, via the lens 1608 and filter1610.

Of the remaining response light, which continues through the dichroic1602 to the polarizing beam splitter 116, specular reflections will havemaintained their P polarization, and will not be reflected by thepolarizing beam splitter 116. However, the scattered response lightshould be randomly polarized. Therefore, approximately half of thescattered response light will be reflected by the polarizing beamsplitter 116 toward the “absorption” detector portion of the system1600. This light then passes through a magnification lens 140 on its wayto a slit 1612. The light passing through the slit 1612 emerges as aline of multi-wavelength light. The center of this line ofmulti-wavelength light corresponds to on-axis light, while light furtherfrom the center of this line corresponds to the light emerging from thetissue 1604 at successive distances from the location of the incidentlight beam spot sourced onto the tissue 1604. This line of lightemerging from the slit 1612 can pass through a dispersion element 146,such as a prism (e.g., PS853, Thorlabs), which can separate the lightinto three lines of distinct wavelengths. The three distinct lines oflight can be redirected by a mirror or lens 1614 and passed through asecond polarizing beam splitter 116 cube, such as to remove any residualP-polarized light, before being projected onto a detector 148, such asan 8×8 two-dimensional PMT light detector array (e.g., H7546B,Hamamatsu). The combined use of a prism 146 (or other dispersiveelement) and a two-dimensional light detector array 148 permitssimultaneous detection of light with multiple wavelengths and differentdepth-sensitivities, such as described above. The system magnificationcan be configured such that the distance between channels on the PMT 2-Darray 148, when projected onto the object plane at the tissue 1604, canbe reduced to the desired source-detector separation distance (e.g., 1.2mm distance, at the array 148, can correspond to 200 μm distance at thetissue 1604). A 24-channel transimpedance amplifier can be coupled tothe outputs of the channels of the PMT array 148, such as to convert thecurrent output of each PMT channel into a voltage signal. In anillustrative example, the system 1600 can use four 8-channelsimultaneous sampling data acquisition boards (e.g., NI PCI-6133,National Instruments, 3 MHz sample rate per channel) to sample thesignal from each of the 24 channels (3 lines) on the 2D array PMT, and 7channels on the linear fluorescence PMT. Acquisition speed can belimited by the galvanometric scanners (average maximum speed, about 4500lines per second). Therefore, 100×100 source-position data can beacquired at 45 frames per second (fps), and 40×40 source-position datacan be acquired at over 100 fps. The 8^(th) channel on the fluorescencedata acquisition card can be used to monitor the position of thex-galvanometer mirror.

Synchronization and control of the LOT system 1600 can be achieved usinga Matlab Graphical User Interface, in an example. The control softwareallows the user to change one or more parameters such as the field ofview, pixels per frame, frame rate, or number of lasers used. Followinga scan, the measured data can be processed in hardware or software, suchas by a signal processor or other circuit 160, into an image (or any ofthe plurality (e.g., 32) of simultaneously acquired images) anddisplayed on a screen, such as a display provided by a user interface162, such as described above with respect to FIG. 1. Analysis forconverting the images into 3D reconstructions can be performed offline,such as described above and in: (1) Hillman, E. M., et al., Laminaroptical tomography: demonstration of millimeter-scale depth-resolvedimaging in turbid media. Opt Lett, 2004, 29(14): p. 1650-2; (2) Hillman,E. M., et al., Depth-resolved optical imaging and microscopy of vascularcompartment dynamics during somatosensory stimulation. Neuroimage, 2007,35(1): p. 89-104; and (3) Hillman E. M. et al. “Depth-resolved opticalimaging of transmural electrical propagation in perfused heart”, OpticsExpress. 15 (26), 17827-17841 (2007), each of which is incorporatedherein by reference in its entirety, including its description ofconverting the images into 3D reconstructions.

FIG. 17 shows an example of early data acquired using a LOT system toperform multi-spectral acquisition, although this data is fromexperiments in which the multi-spectral acquisition was performedserially, rather than in parallel as described above. In this example,two benign lesions, a mole and amelanotic erythema, were imaged usingLOT. The resulting measurements were merged into red-green-blue images.These images depict LOT data in its “raw” form, representing a series ofboundary measurements for 100×100 source positions for three differentsource-detector separations. This data can be substantially downsampledbefore 3D LOT “reconstruction” such as to discern invasion depth or toquantitatively extract HbO, HbR, or melanin concentrations. However,these raw images of FIG. 17 demonstrate the significant value of thisnon-contact, high-speed multi-spectral imaging tool.

In FIG. 17, the left-most images show Monte-Carlo simulations of thelikely paths of light for three source-detector separations: (1) 0.2 mm,top left image; (2) 0.6 mm, middle left image; and (3) 1.0 mm, bottomleft image. The middle images in FIG. 17 show 6 mm×6 mm raw imaging dataacquired on a benign mole (A) and amelanotic erythema (B), for the samethree source-detector separations: (1) 0.2 mm, top images; (2) 0.6 mm,middle images; and (3) 1.0 mm, bottom images. The right-most images arephotographs of the mole (A) and amelanotic erythema (B). The middleimages shown in FIG. 17 are red-green-blue merge bitmaps of the datafrom red, green and blue lasers. In these images, the brown melanin andred hemoglobin can clearly be distinguished. The close source-detectorseparations reveal the rough surface of the skin. The wide separationsmore clearly reveal the sub-surface absorbing structure. The blueish hueto the superficial images corresponds to wavelength-dependentback-scatter.

In FIG. 17, the close source-detector separations can reveal featuresnear the surface of the skin. The wider source-detector separations canenhance visualization of sub-surface structures, even without subsequent3D analysis. In FIG. 17, the mole image data (A) shows brown melanin ineach source-detector separation image. In FIG. 17, the amelanoticerythema image data (B) lack melanin, but show red hemoglobin contrast.In FIG. 17, the amelanotic erythema data (B) also indicate that thehemoglobin was not present at the surface of the skin, which isconsistent with the vasculature of the skin. This data demonstrates thatmulti-wavelength LOT can provide highly valuable clinical information.Clinical trials can be undertaken to acquire LOT measurements onpatients with LM or LMM before surgical excision. This canquantitatively compare our “raw” and reconstructed in-vivo data to thehistology of the same excised tissue to further help establish thediagnostic or prognostic potential of LOT for this application.

FIG. 18 shows an example of simultaneously-acquired multi-spectral LOTdata obtained using a test phantom as the object being imaged. FIG. 18shows examples of cross-sectional and overhead views of the testphantom. A mixture of intralipid, agarose, and bovine hemoglobin wasprepared and disposed at various depths (e.g., 0.2 mm, 0.4 mm, and 0.6mm) of the phantom. The modeled sensitivity functions in FIG. 18correspond to different source-detector separations distances (e.g.,0.25 mm, 0.5 mm, and 1.0 mm), and can be used for image reconstruction,such as described above, to produce the correspondingsimultaneously-acquired multi-spectral RGB Merged LOT Data of FIG. 18.The simultaneously-acquired multi-spectral RGB LOT Data of FIG. 18demonstrates that a wider source-detector separation can exhibit abetter contrast to a deeper object, and the narrower source-detectorseparation can exhibit a better contrast to shallower object.

Notes

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” All publications, patents, and patent documentsreferred to in this document are incorporated by reference herein intheir entirety, as though individually incorporated by reference. In theevent of inconsistent usages between this document and those documentsso incorporated by reference, the usage in the incorporated reference(s)should be considered supplementary to that of this document; forirreconcilable inconsistencies, the usage in this document controls.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein.” Also, in the following claims, theterms “including” and “comprising” are open-ended, that is, a system,device, article, or process that includes elements in addition to thoselisted after such a term in a claim are still deemed to fall within thescope of that claim. Moreover, in the following claims, the terms“first,” “second,” and “third,” etc. are used merely as labels, and arenot intended to impose numerical requirements on their objects.

Method examples described herein can be machine-implemented orcomputer-implemented at least in part. Some examples can include atangible computer-readable medium or machine-readable medium encodedwith instructions operable to configure an electronic device to performmethods as described in the above examples. An implementation of suchmethods can include code, such as microcode, assembly language code, ahigher-level language code, or the like. Such code can include computerreadable instructions for performing various methods. The code may formportions of computer program products. Further, the code may be tangiblystored on one or more volatile or non-volatile computer-readable mediaduring execution or at other times. These computer-readable media mayinclude, but are not limited to, hard disks, removable magnetic disks,removable optical disks (e.g., compact disks and digital video disks),magnetic cassettes, memory cards or sticks, random access memories(RAMs), read only memories (ROMs), and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. § 1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription, with each claim standing on its own as a separateembodiment. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

What is claimed is:
 1. An imaging device, comprising: an objective; alight source; a scanning/de-scanning optical assembly having a firstmoving light-redirecting element that routes illumination light from thelight source, through the objective in a proximal-to-distal direction,and scans a resulting beam across a target region; a light detector witha one or two dimensional array of detector elements, each providing arespective luminance signal; the scanning/de-scanning optical assemblybeing arranged with respect to the objective, the light source, and thelight detector such that after light received from the target regionpasses through the objective in a distal-to-proximal direction, thefirst moving light-redirecting element routes the received light to thelight detector such that optical responses arising at multiple depths inthe target region are concurrently imaged onto respective differentdetector elements within the light detector, such that a resulting imageresolves depth information about the optical responses at the multipledepths, with optical responses obtained at distances that are fartherfrom the incident light beam location corresponding to light that haspenetrated more deeply into the target region.
 2. The device of claim 1,further comprising a processor connected to the light detectorprogrammed to calculate, from the luminance signals, a distribution ofthe optical responses at the multiple depths.
 3. The device of claim 1,wherein the first moving light-redirecting element scans the resultingbeam across the target region and de-scans received light from theregion of interest to maintain a position of an image of the imageregion of interest on the light detector as the resulting beam isscanned such that the region of interest moves across the target regionas the resulting beam is scanned.
 4. The device of claim 1, furthercomprising a beam splitter arranged to (a) route the illumination lightso that the illumination light will travel through the objective in aproximal-to-distal direction and (b) route received light, which haspassed through the objective to in a distal-to-proximal direction,towards the light detector.
 5. The device of claim 4, wherein the beamsplitter is a dichroic beam splitter and a wavelength of the lightsource is selected to excite fluorescence in a predefined fluorescingmaterial selected by the properties of the dichroic beam splitter. 6.The device of claim 1, wherein the scanning/de-scanning optical assemblyhas a second light-redirecting element, the first and secondlight-redirecting elements moving independently to scan acrossrespective lateral dimensions of the target volume.
 7. The device ofclaim 1, wherein the illumination light enters the target region with anangle of incidence between 10° and 80°.
 8. The device of claim 1,wherein the illumination light enters the target region with an angle ofincidence between 10° and 50°.